It is known in the art to have load-bearing racks for mounting on pick-up truck beds to extend the utility and load-bearing capacity of the truck. For example, DeFreze in U.S. Pat. No. 4,138,046 describes a rack mounted in the four corners of the truck bed and raised above the truck cabin to facilitate loads with dimensions beyond those of the truck bed, readily assembled and disassembled for compact storage and reasonably quick installation. Dublin in U.S. Pat. No. 4,423,899 describes a rack system permanently mounted in a truck bed at its corners with versatile attachments thereto for various load options. Both patents require support pillars in the corners of the truck bed which precludes use of these racks when the truck is outfitted with a conventional truck bed canopy. Commercial racks are also available; for example, Sears on page 803 of their 1989 catalog shows a ladder rack usable with a truck bed canopy, the rack being supported by a base that bolts onto the inside of the truck bed and extends under the canopy and outside of the bed. All of these racks require defacing of the truck bed by welding or bolting rack support bases to the inside of the truck bed. None of these racks are adjustable in size .